We use the VC motorneurons to investigate the molecular mechanisms regulating axon outgrowth and branching. VC neurons display a simple bipolar morphology with axons projecting along the ventral nerve cord and branching at the vulva. We are undertaking a genetic screen to identify VC axon outgrowth mutants using a
cat-1::gfp reporter to label VC4 and VC5 neurons. So far, two classes of mutants that alter the normal bipolar morphology of VC neurons have been identified: mutants displaying a tripolar morphology and those displaying a single neurite morphology. We mapped one complementation group (2 alleles) that displayed a highly penetrant tripolar VC phenotype to a small interval on LGX near B0410.2, a homolog of the cell polarity gene Strabismus/Van Gogh (referred to as Stbm). We confirmed Stbm as our gene by rescuing with a genomic PCR fragment containing a single open reading frame and identifying sequence alterations in our mutants. Because Stbm acts in a Wnt signalling pathway to regulate planar cell polarity (PCP) and gastrulation movements in flies and vertebrates we are examining VC axon morphology in Wnt and PCP mutants to determine if C. elegans Stbm acts in a similar pathway to regulate VC neurite outgrowth or polarity. A preliminary characterization of
tm306, a mutation in the PCP gene Flamingo (F15B9.7) (a gift from S. Mitani), however did not reveal defects in VC axon guidance or morphology. We will present our genetic and molecular characterization of Stbm and other mutants arising from the screen.